Is simply covering the patient's mouth with a surgical mask during transnasal endoscopy sufficient as an anti-COVID-19 measure? - Yohei Nose; Tomo Ishida; Tomoki Makino; Tsuyoshi Takahashi; Yukinori Kurokawa; Hidetoshi Eguchi; Yuichiro Doki; Kiyokazu Nakajima (Korean Society of Gastrointestinal Endoscopy, 2023)